Figure 8.11 This patient presented with restenosis at follow‐up after stent implantation in the right coronary artery (arrows on angiogram and telling angiotomography images, top panel). On IVUS, all stent struts are seen at proximal and distal references (e.g. 20 mm and 25 mm), whereas at the fracture site there is superficial calcification from 11 to 4 o’clock and no stent strut is seen (arrow).
Guidance for stent implantation
Stent sizing
Pre‐interventional IVUS is performed to assess stenosis severity and plaque composition and distribution, measure reference vessel size, and measure lesion length. As a result, stent size can be chosen more accurately than solely by angiography. There are a number of paradigms that can be used. Stent size can be selected by identifying the maximum reference lumen diameter (proximal or distal to the lesion); it results in stent upsizing without an increase in complications. At the other extreme, stents can be sized to the “true vessel,” “media‐to‐media,” or mid‐wall dimensions to reflect the amount of angiographically silent disease and, in most cases, the extent of positive remodeling, not just vessel size. Typically, this measurement will be larger than reference lumen reference and, thus, should be used only by experienced operators who understand its limitations.
IVUS measures lesion length more accurately than angiography because IVUS eliminates foreshortening, vessel tortuosity, or bend points.
Stent expansion and malapposition
IVUS studies have shown that lumen enlargement after stent implantation is a combination of vessel expansion and plaque redistribution/embolization, not plaque compression [36–38]. Plaque reduction in patients with acute coronary syndromes is attributed to plaque or thrombus embolization [38]. Intrusion or prolapse of plaque through the stent mesh into the lumen is more common in acute coronary syndromes and in saphenous vein graft lesions. Importantly, after stent implantation there is a significant residual plaque burden behind the stent struts that almost always measures 50–75% at the center of the lesion. Thus, the stent CSA always looks smaller than the EEM even when the stent is fully expanded. Stent expansion describes the minimum stent CSA either as an absolute measure (absolute expansion), or compared with the predefined reference area – proximal, distal, largest, or average reference area – (relative expansion). Greater absolute stent expansion has been associated with better long‐term stent patency, better clinical outcomes and a lower risk of stent failure [4–5, 39]. Intravascular ultrasound studies have been relatively consistent in showing that a stent cross‐sectional area of 5.5 mm2 best discriminates subsequent events in non‐left main lesions. For LM lesions, cut‐offs values are higher (e.g. >7 mm2 for distal LM and >8 mm2 for proximal LM by IVUS) [4–5, 40,41].
The recent expert consensus suggests that the cut‐off >80% for the MSA (relative to average reference lumen area) appears to be a reasonable approach to adopt in clinical practice [4,5].
Apposition refers to the contact between the stent struts to the arterial wall. Incomplete stent apposition is defined as one or more struts clearly separated from vessel wall with evidence of blood speckles behind the strut. There is no conclusive evidence suggesting that isolated acute incomplete stent apposition (in the absence of concomitant underexpansion) is associated with adverse clinical outcomes. Identifiable causes of restenosis other than intimal hyperplasia include chronic underexpansion (18–40%) stent fracture (<5%) and neoatherosclerosis [4,5].
Clinical outcomes using IVUS for non‐LMCA and LMCA PCI
The two main uses of IVUS are to insure optimal stent expansion (stent CSA) and full coverage of the lesion. Stent underexpansion is a powerful predictor of early stent thrombosis and restenosis after DES implantation according to numerous IVUS studies [4,5,42–49]. In almost every meta‐analyses, IVUS guidance was associated with a reduction in death (primarily cardiovascular mortality) as well as other hard end points of myocardial infarction and stent thrombosis. Of note, the beneft of IVUS guidance in reducing events after DES implantation was greater in meta‐analyses of randomized trials of IVUS vs angiographic guidance compared to meta‐analyses of registries, and it tended to be greater in high‐risk patient and complex lesion subsets than in “all comers” populations [46].
A meta‐analysis of outcomes after IVUS‐guided vs. angiography‐guided DES implantation in 26 503 patients enrolled in three randomized trials and 14 observational studies, demonstrated that IVUS‐guided PCI was associated with a significantly lower risk of TLR (OR 0.81; p = 0.046). In addition, the risk of death (OR 0.61; p <0.001), MI (OR 0.57; p <0.001), and stent thrombosis (OR; p <0.001) were also decreased [47]. A recent metanalysis of 10 RCTs (5007 participants, which include the largest RCTs IVUS‐XPL and ULTIMATE Trial) including patients with CTO, stable ischemic heart disease or presented as ACS showed that routine use of IVUS was effective in reducing TLR (RR 0.59; p < 0.01), TVR (RR 0.59; p < 0.01), and MACE (RR 0.63; p < 0.01). Cardiovascular mortality was also significantly reduced (RR 0.51; p = 0.04) [48].
Clinical outcomes using IVUS for LMCA PCI
Observational Studies
Observational studies overall provide robust evidence of benefit for intracoronary imaging. A multicenter revascularization for unprotected left MAIN coronary arterystenosis: COMparison of Percutaneous coronary Angioplasty versus surgical Revascularization (MAIN‐COMPARE) [50] registry of LMCA interventions showed that patients treated with IVUS‐guided DES implantation had better three year survival than patients in whom IVUS was not used to guide LMCA DES implantation (4.7% vs 16.0%, p = 0.048). A pooled analysis of four Spanish registries examined the outcomes of 1670 LMCA PCI patients. By means of matching, 505 patient pairs were constructed and survival free of cardiac death, MI, and target lesion revascularization at 3 years was 88.7% in the IVUS group and 83.6% in the non‐IVUS group (p =0.04) [51].
In a single‐center analysis by Gao et al. including consecutive patients with unprotected LMCA stenosis who underwent DES implantation, unadjusted MACE rates at one year follow‐up were significantly lower in the IVUS‐guided group. These findings were consistent after propensity‐score matching, driven by a reduction in cardiac death and target vessel revascularization (TVR) [52].
In another study, using the Swedish Coronary Angiography and Angioplasty Registry (SCAAR), both a retrospective and a propensity‐matched analysis of 2468 patients, the authors showed that at 10 years of follow‐up, IVUS guidance reduced mortality compared to angiographic guidance from 62.1 to 32.5% (HR = 0.44) overall and from 56.6 to 33.7% (HR=0.57) in propensity score‐matched patients [53].
Recently, a single‐center registry of 6005 patients assessed the impact of IVUS‐guided PCI on long‐term (64 months median follow‐up) in patients undergoing PCI for complex lesions (11.4% LMCA PCI). IVUS guidance was associated with a reduction in cardiac mortality both overall, in every patient subgroup, and in almost every lesion subgroup. Overall, IVUS‐guided DES implantation was associated with a signifcantly lower risk of cardiac death compared with angiography‐guided DES implantation (10.2% vs 16.9%; HR = 0.57, p<0.001) [54].
The largest observational study so far involved an analysis from the British Cardiovascular Intervention Society (BCIS) database. Imaging guidance (mostly IVUS) for LMCA PCI increased from 30.3% in 2007 to 50.2% in 2014. Of note, imaging guidance was associated with lower 30‐day and 12‐month all‐cause mortality rates. Operators with greater LMCA PCI volumes had greater mortality reductions when these operators used IVUS guidance [55].
